1. Field of the Invention
The invention relates to an electrical junction box for a solar cell module of solar cells which are connected with thin conductor strips, with a housing and electrical and/or electronic means provided in the housing, and at least one electrical connection device which has at least one terminal means and which is provided in the housing.
2. Description of Related Art
Since the output voltage of individual solar cells is generally too low to operate electrical devices, such as household appliances or similar devices, generally, several solar cells are interconnected to form solar cell modules. In this regard, on the one hand, there is the possibility of series connection of the solar cells, and on the other, the possibility of parallel connection of the solar cells in the solar cell module. The individual currents of the solar cells are added to one another to form the overall current by parallel connection of the solar cells. In this connection, the solar cells connected in parallel should have essentially the same physical properties so that, in practice, the parallel connection of solar cells has hardly become common, especially also since an individual solar cell can already deliver a current of a few amperes.
In the assembly of solar cell modules with individual solar cells, the solar cells are therefore often series-connected. However, a problem can arise when a solar cell module is partially shadowed, therefore a solar cell or individual solar cells of the solar cell module receive less or no solar radiation at all. The reason for reduced solar radiation can be, for example, fouling of the solar cells or shadows cast by trees, building parts or buildings.
In contrast to shadowing of the solar module uniformly over its entire surface, which leads only to a reduction in output, the following problem arises with partial shadowing: A common current flows through the series-connected solar cells of the solar cell module, each individual solar cell with its respective voltage contributing to the total voltage of the solar cell module. If, at this point, one solar cell is shadowed, it no longer produces voltage and essentially a diode in the reverse direction opposes the current flow in the solar cell module. However, this means that the entire module can no longer deliver current, so that the overall operation of the solar cell module is adversely affected.
Moreover, it applies that there is a voltage on the shadowed solar cell which is dependent on the position of the shadowed solar cell in the series connection. If the voltage on the shadowed solar cell is greater than its blocking voltage, a breakdown occurs in the solar cell, and thus, the solar cell is permanently damaged. Even if the solar cell should not be damaged by the breakdown, a large power loss is converted in the shadowed solar cell so that the shadowed solar cell heats up. This heating can also lead to damage to the shadowed solar cell and to the solar cells adjacent to it.
In order to avoid the problems associated with the partially shadowed solar cells, diodes, so-called bypass diodes, which are connected anti-parallel to the solar cells are often used. This results in that a shadowed solar cell no longer supplies a portion to the overall voltage of the solar cell module, but the current flow is nevertheless maintained. The solar cell module thus shows only a reduced operating voltage, but does not fail completely. Moreover, in the shadowed solar cell, power is no longer converted, so that damage to the shadowed solar cell can be avoided.
Basically, each solar cell of a solar cell module could be assigned exactly one diode. However, often it happens that a plurality of series-connected solar cells is safeguarded by a respective common diode. Electrical junction boxes which are used for solar cell modules thus, generally, always have a plurality of bypass diodes. Moreover, in the electrical junction boxes, there can be other electrical and/or electronic means so that the conductors fed to the electrical junction box must be connected to electrical and/or electronic means, such as bypass diodes.
The solar cells in a solar cell module are generally connected to one another with thin conductor strips, so-called strings. These conductor strips typically have a thickness of a few tenths of a millimeter (roughly 0.3 mm) and a width of a few millimeters (roughly 3-8 mm). These conductor strips which connect the individual solar cells of the solar cell module to one another are routed out of the solar cell module so that thin conductor strips can be used directly for connection purposes.
The bypass diodes are generally located on a circuit board which is connected to the connection device of the junction box. The connection device is connected to the solar cell module via at least one conductor strip.
For connection, the conductor strips are typically routed from underneath into the electrical junction box which has a removable cover, so that the individual conductor strips can be brought by hand into contact with the electrical connection device provided in the housing of the junction box. To do this, the thin conductor strips coming from underneath from the solar cell module relative to the housing of the junction box are generally bent by 180° in order to then be connected coming from overhead, for example, via a clamping means to the terminal device. This bending is easily possible since the thin conductor strips which typically are made of metal are very flexible as a result of their dimensions, especially specifically their low thickness. In any case, this procedure is very complex and time-consuming, and connection faults cannot be easily avoided. Moreover, in the known junction box, it is disadvantageous that, based on the limited external dimensions of the housing generally within the junction box, the electrical and/or electronic means and the connection device must be located very near one another. For this reason, only a very small free space is available for connecting the conductor strips; this makes connection difficult.